1. Field of the Invention
The present invention relates generally to the field of pipe connections, and in particular, to a dual function, self restraining and sealing system that is used to form a secure pipe connection between two plastic pipes and to a method of manufacturing the same.
2. Description of the Related Art
Pipes are commonly used for the conveyance of fluids under pressure, as in city water lines. They may also be used as free-flowing conduits running partly full, as in drains and sewers. Pipes for conveying water in appreciable quantities have been made of steel, cast iron, concrete, vitrified clay, and most recently, plastic including the various polyolefins and PVC.
It is well known in the art to extrude plastic pipes in an elongated cylindrical configuration of a desired diameter and to then cut the extruded product into individual lengths of convenient size suitable for handling, shipping and installing. Each length of pipe is enlarged or “belled” at one end sufficiently to join the next adjacent pipe section by receiving in the female, belled end the unenlarged or “spigot” male end of the next adjacent length of pipe. The inside diameter of the bell is formed sufficiently large to receive the spigot end of the next section of pipe with sufficient clearance to allow the application of packing, caulking, elastomeric gaskets or other sealing devices designed to prevent leakage at pipe joints when a plurality of pipe lengths are joined to form a pipeline.
During a standard installation of a pipeline, in, for example, municipal installations, the joints between pipes and between pipes and fittings must be restrained to accommodate varying pressures as well as environmental influences. For example, there are various types of fitting connections which are commercially available and which are used in, for example, the waterworks industry. In one type of connection, the current restraint mechanism is an external clamping device which is totally separated from the sealing function. Thus, a separate mechanism must perform the sealing function. In another type of fitting connection, a gasket performs the sealing function. However, it is necessary that an external means must compress the gasket by mechanical action such as T-bolts. Most current restraining systems offered in the industry require a substantial amount of labor to install. Under most installation conditions, the restraining systems are cumbersome to install and represent a substantial additional effort for the contractor. As a result, these and other traditional restraining mechanisms of the prior art add considerable cost and complexity to the pipe installation as well as adding the possibility of human error depending upon the specific field conditions and applications.
In the early 1970's, a new technology was developed by Rieber & Son of Bergen, Norway, referred to in the industry as the “Rieber Joint.” The Rieber system provided an integral sealing mechanism within the belled or female pipe end for sealing with the spigot end of a mating pipe formed from thermoplastic material. In the Rieber process, the elastomeric gasket was inserted within an internal groove in the socket end of the female pipe as the female or belled end was simultaneously being formed. The provision of a prestressed and anchored elastomeric gasket during the belling process at the pipe factory provided an improved socket end for a pipe joint with a sealing gasket which would not twist or flip or otherwise allow impurities to enter the sealing zones of the joint, thus increasing the reliability of the joint and decreasing the risk of leaks or possible failure due to abrasion. The Rieber process is described in the following issued United States patents, among others: U.S. Pat. Nos. 4,120,521; 4,061,459; 4,030,872; 3,965,715; 3,929,958; 3,887,992; 3,884,612; and 3,776,682. While the Rieber process provided an improved sealing system for plastic pipelines of the type under consideration, it did not include any integral restraint type mechanism.
Accordingly, there has continued to exist a need for a cost-effective, easy to manufacture and use combination seal and restraint system for restraining and sealing plastic pipe against internal and external forces at a pipe or fitting connection and for joining and sealing at least two plastic pipes at a pipe joint to form a pipeline which system is internal to the pipes themselves, rather than relying upon external connecting elements.
Applicant's now issued U.S. Pat. No. 7,284,310 addressed many of the above noted deficiencies in the prior art. The device described in the '310 patent included an improved restraining and sealing mechanism which was internal to the pipes being joined, rather than relying upon external restraint mechanisms. The restraining and sealing mechanism included a circumferential housing and a companion sealing ring which were both received within a mating groove provided in the belled end of a female pipe. The circumferential housing has an interior region which contains a gripping ring insert. The sealing ring and housing were integrally located within a belled pipe end during belling operations. Insertion of a mating male pipe end within the female, belled pipe end formed a secure pipe connection.
Despite the advances in the art represented by the device described in the '310 patent, a need continues to exist for further advances in the technology.